Method of joining lined pipes

ABSTRACT

Two outer steel pipes ( 16  and  16 A) are each lined by corrosion resistant lining pipes ( 18  and  18 A) of compressible plastics material which stop short of the ends ( 20, 20 A) of the outer pipes to leave an annular recess or counterbore ( 24  and  24 A) at each of those ends. A tubular bridging-member ( 2 ) of ductile, plastically deformable, corrosion resistant material, for example brass or stainless steel has two tubular end portions ( 4  and  6 ) extending in opposite directions from an intermediate tubular portion ( 8 ) having an outer diameter greater than that of the end portions ( 4  and  6 ) and an inner diameter greater than that of the said end portions. The end portions ( 4  and  6 ) are encircled by ribs ( 12 ). Initially the outer diameter of the end portions ( 4, 6 ) is less than that of the inner diameter of the lining pipes ( 18, 18 A). Thus each lined pipe ( 16, 16 A) can be fitted over the respective end portions ( 4  and  6 ) with the intermediate portion ( 8 ) occupying the combined counterbore ( 24, 24 A). A tool applied internally, radially expands the end portions ( 4  and  6 ) to compress the plastics lining pipes ( 18, 18 A) against the outer pipes ( 16, 16 A) by an amount in the range of 8% to 30% of the wall thickness of the lining pipes. Then adjacent ends ( 20, 20 A) of the outer pipes are welded together at  28 . The outer surface of the intermediate portion ( 8 ) can carry heat insulation material. The bridging-member ( 2 ) preserves the integrity of the internal corrosion resistance across the joint between the outer pipes.

This invention relates to a method of joining pipes lined with corrosionresistant plastics material.

Carbon steel pipelines are provided with liners of corrosion resistantplastics material so that the pipeline can be used to convey aggressivemedia. The provision of such liners avoids the need to use expensivestainless steel pipes.

An object of the invention is to provide a method capable of being usedto provide a corrosion resistant barrier internally across a jointbetween two adjacent pipes each internally lined with corrosionresistant plastics material.

According to the invention a method of joining pipes lined withcorrosion resistant plastics material comprises providing a first outerpipe lined by a first lining pipe of corrosion resistant compressibleplastics material having an end face spaced internally of the firstouter pipe from an end of said first lining pipe whereby said firstouter pipe and said lining pipe combination has a first counterboreadjacent to said end of the first outer pipe, providing a tubularbridging-member of plastically deformable, corrosion resistant ductilematerial, said bridging-member comprising a tubular first end portionand an opposite tubular second end portion each extending in an oppositedirection to the other from an intermediate tubular portion having anexternal diameter greater than that of the first or second tubular endportion and an internal diameter greater than that of first or secondtubular end portions, introducing said first tubular end portion of thebridging-member into said first lining pipe and said intermediateportion into said first counterbore, providing a second outer pipe linedby a second lining gripe of corrosion resistant compressible plasticsmaterial having an end face spaced internally of the second outer pipefrom an end of said second outer pipe whereby said second outer pipe andsaid second lining pipe combination has a second counterbore adjacentsaid end of the second outer pipe, introducing said second tubular endportion of the bridging-member into said second lining pipe and saidintermediate portion into said second counterbore whereby said ends ofthe first and second outer pipes are adjacent, at a time after saidfirst tubular end portion is introduced into said first lining pipeexpanding the first tubular end portion transversely to its tube axis soas to press the first tubular end portion into the first lining pipewhich is compressed between the first outer pipe and said first tubularend portion, at a time after said second tubular end portion isintroduced into said second lining pipe expanding the second tubular endportion transversely to its tube axis so as to press the second tubularend portion into the second lining pipe which is compressed between saidsecond outer pipe and said second tubular end portion, and at a timeafter said ends of the first and second outer pipes are brought intoadjacency said outer pipes being joined together externally of saidlining pipes.

Each outer pipe may be of metal, for example a ferrous metal. Theferrous metal may be steel, for example carbon steel.

Each lining pipe may formed of thermoplastic plastics material.

Each lining pipe may be formed of a polyolefin, or a polyethylene, or apolyvinylidene fluoride.

A said lining pipe may be inserted into a said outer pipe by firstcompressing the outer diameter of the lining pipe, then drawing thelining pipe into the outer pipe and allowing the lining pipe to resileor re-expand to substantially its original external diameter so as tofit relatively closely against the inner wall of the outer pipe.

The bridging-member may be formed of a corrosion resistant metal, forexample brass or stainless steel.

The invention will now be further described, by way of example; withreference to the accompanying drawings in which:

FIG. 1 is a cross-section of a bridging-member used in the methodaccording to the invention;

FIG. 2 is a cross-section to illustrate a stage in the method accordingto invention using the bridging-member in FIG. 1;

FIG. 3 is a cross-section to illustrate two outer pipes and theirlinings joined by the method according to invention in which thebridging-member in FIG. 1 is used, and

FIG. 4 is a cross-section of another embodiment of the bridging-memberfor use in the method according to the invention.

In FIG. 1 a bridging-member 2 is formed of plastically deformable,ductile material of good corrosion resistance and capable ofwithstanding permanent plastic strains of, for example, 3%. Thebridging-member 2 may be corrosion resistant metal, for example brass orstainless steel. The bridging-member 2 is of an open ended tubular formhaving substantially cylindrical tubular end portions 4 and 6 extendingin opposite directions from an intermediate or central tubular portion 8which in cross-section is rather like a humped-back bridge. Each endportion 4, 6 curves, flares or blends at 10 into the central portion 8which has an internal diameter greater than that of the tubular endportions 4, 6 and an outer diameter greater than that of said tubularend portions 4, 6. Each tubular end portion 4, 6 has on its outersurface a plurality of integral excrescences 12 axially spaced apart byflat bottomed groves 14. The excrescences 12 may each be of asubstantially castellated cross-sectional shape and may have slopingsides and rounded top corners, and each excresence is preferably in theform of a continuous annular rib extending around the respective endportion 4 or 6.

With reference to FIG. 2 an outer pipe 16 is formed of metal, preferablya weldable metal, for example cast steel. The pipe 16 is lined with alining pipe 18 of corrosion resistant plastics material, for examplepolyethylene, installed in the pipe 16 by any suitable known means. Thelining pipe 18 may have any desired length, for example it may be abouttwenty four meters in length. The outer pipe 16 has an end 20. Thelining pipe 18 is so formed that it has an end face 22 spaced axiallyback internally of the outer pipe 16 so that the pipe combinations 16,18 has an annular recess or counterbore 24 at the end 20 of the pipecombination. The counterbore 24 may result from inserting the liningpipe 18 into the pipe 16 so the lining pipe is spaced from the pipe end20, or the installed lining pipe may be cut back from the pipe end 20 toform a counterbore 24 of desired size.

The tubular end portion 4 of the bridging-member 2 is inserted into thelining pipe 18 through pipe end 20 so that substantially half the axiallength of the central tubular portion 8 occupies the counterbore 24, andthe end face 22 and central portion 8 are in abutement. Now a radiallyexpansible tool 26 of any suitable known kind which may be operatedhydraulically or mechanically is inserted into the tubular end portion4.

In FIG. 2 the tool 26 is expanded to radially expand the tubular endportion 4 thereby expanding the outer diameter of the tubular endportion 4 causing the tubular end portion 4 of the bridging-member 2 tobecome embedded into the inner surface of the lining pipe 18 andcompress the lining pipe against the outer pipe 16 (see FIG. 3). Theradial expansion of the tubular end portion 4 has the effect of bracingthe central portion 8 of the bridging-member 2 against the inner surfaceof the outer pipe 16.

Now, continuing with FIG. 3, another outer pipe 16A with its plasticslining 18A and counterbore 24A at pipe end 20A is fitted over thetubular end portion 6 and other half of the central portion 8 of thebridging-member 2, and the expansible tool 26 (FIG. 2) is used toradially expand the tubular end portion 6 against and into the liningpipe 18A. Then the two adjacent pipe ends 20, 20 of the outer pipes canbe welded together in an annular weld joint 28.

If desired, the pipes 16, 16A may be welded together before the endportions 4 and 6 are radially expanded. Those end portions 4 and 6 maybe radially expanded in any order before or after the welding, or may beexpanded simultaneously. The expanding tool 26 may also serve as a guideor former for aligning the pipes 16 and 16A prior to welding.

The wall thickness of each lining pipe 18, 18A may be compressed by anydesired amount, though the preferred range is a compression of between8% to 30%. The bridging-member 2 is capable of being used with a typicalrange of lined pipe tolerances by reason of controlling the forceapplied by the tool 26 rather than by varying the extent of its radialexpansion.

The bridging-member 2 preserves the integrity of the anti-corrosioninterior of the joined pipes 16 and 16A by extending internally acrossthe joint between those two pipes and being in substantially fluid-tightrelation with the lining pipes 18 and 18A.

If desired the intermediate portion 8 of the bridging-member 2 may besurrounded externally by heat insulating material to impede the passageof heat from the pipe joint welding process into the plastics pipes 18and 18A which may be damaged by the welding heat.

In FIG. 4 the bridging-member 2 has an intermediate portion 8 of reducedwall thickness compared with that in FIG. 1. The intermediate portion 8in FIG. 4 is surrounded by a ring 30 of plastics material carrying onits outer side a ring of heat insulating material 32. The rings 30, 32may be attached to the intermediate portion 8, for example by adhesive.Or the ring 30 with the heat insulation 32 may be placed about theintermediate portion 8 after one of the tubular end portion 4 or 6 hasbeen inserted into one of the lining pipes 18 or 18A.

What is claimed is:
 1. A method of joining pipes lined with corrosionresistant plastics material comprising: providing a first outer pipelined by a first lining pipe of corrosion resistant compressibleplastics material having an end face spaced internally of the firstouter pipe from an end of said first outer pipe whereby said first outerpipe and said first lining pipe combination has a first counterboreadjacent to said end of the first outer pipe; providing a tubularbridging-member of plastically deformable, corrosion resistant ductilematerial, said bridging-member comprising a tubular first end portionand an opposite tubular second end portion each extending in an oppositedirection to the other from an intermediate tubular portion having anexternal diameter greater than that of the first tubular end portion orsecond tubular end portion and an internal diameter greater than that offirst tubular end portion or second tubular end portion; introducingsaid first tubular end portion of the bridging-member into said firstlining pipe and said intermediate portion into said first counterbore;providing a second outer pipe lined by a second lining pipe of corrosionresistant compressible plastics material having an end face spacedinternally of the second outer pipe from an end of said second outerpipe whereby said second outer pipe and said second lining pipecombination has a second counterbore adjacent said end of the secondouter pipe; and introducing said second tubular end portion of thebridging-member into said second lining pipe and introducing saidintermediate portion into said second counterbore, whereby said ends ofthe first and second pipes are adjacent, at a time after said firsttubular end portion is introduced into said first lining pipe expandingthe first tubular end portion transversely to its tube axis so as topress the first tubular end portion into the first lining pipe which iscompressed between the first outer pipe and said first tubular endportion, at a time after said second tubular end portion is introducedinto said second lining pipe expanding the second tubular end portion,transversely to its axis so as to press the second tubular end portioninto the second lining pipe which is compressed between said secondouter pipe and said second tubular end portion, and at a time after saidends of the first and second outer pipes are brought into adjacency saidouter pipes being joined together externally of said lining pipes.
 2. Amethod as claimed in claim 1, wherein each of said tubular end portionscarries external excrescences.
 3. A method as claimed in claim 2,wherein said excrescences comprise a plurality of axially spaced annularribs.
 4. A method as claimed in claim 1, wherein the bridging-membercomprises metal.
 5. A method as claimed in claim 4, wherein the metalcomprises brass or stainless steel.
 6. A method as claimed in claim 1,wherein the intermediate tubular portion of the bridging-member issurrounded by heat insulation material.
 7. A method as claimed in claim6, further comprising placing the heat insulation material around theintermediate tubular portion after the first tubular end portion of thebridging-member is introduced into the first lining pipe.
 8. A method asclaimed in claim 6 wherein the heat insulation material is provided atan outer side of a ring.
 9. A method as claimed in claim 1, wherein theintermediate tubular portion of the bridging-member includes a side facewhich can come into abutment with one of said end faces.
 10. A method asclaimed in claim 1, wherein the outer pipes comprise a weldable materialand are joined together by welding.